In general, batteries are configured to obtain electric energy by using chemical or physical reaction. Here, chemical batteries are classified into primary and secondary batteries. That is, single-use batteries such as manganese batteries, alkaline batteries, and mercury batteries are called primary batteries, and rechargeable batteries such as rechargeable batteries or lead storage batteries are called secondary batteries.
Secondary batteries may be variously classified according to the structure of an electrode assembly. For example, secondary batteries may be classified into a stacking-type, a winding-type (a jelly-roll-type), or a stacking/folding type according to the structure of the electrode assembly. In the stacking type structure, each of a negative electrode, a separator, and an positive electrode is cut to a predetermined size, and then, the cut negative electrode, separator, and positive electrode are successively stacked to form an electrode assembly. Here, the separator is disposed between the negative electrode and the positive electrode. In the winding-type structure, each of a negative electrode, a separator, an positive electrode, and a separator is formed in a sheet shape, and then, the negative electrode, the separator, the positive electrode, and the separator are successively stacked and wound to form an electrode assembly. In the stacking/folding type structure, a full cell or bicell is formed and then wound through a separator sheet to form an electrode assembly. Here, each of a negative electrode, a separator, and an positive electrode is cut to a predetermined size, and then, the cut negative electrode, separator, and positive electrode are successively stacked to form the full cell or bicell (the full cell or the bicell includes at least one negative electrode, separator, and positive electrode).